Vacuum coating of substrates by the electron-beam evaporation process generally involves the practice of slowly rotating a substrate holder with respect to an offset or centrally positioned evaporation source, thereby providing for more uniform and even coating. In one example of such practice, the substrates are loaded into counter-bored holes in a holder, such as a domed disc that is placed on a carrier platform. The carrier is then transferred from atmosphere through suitable locks or chambers into the high vacuum coating zone, where it is positioned beneath a mechanism for first lifting the substrate holder from, and holding it above the carrier; the mechanism then rotates the holder with respect to a conical coating pattern or the like. Prior to substrate rotation the carrier is removed from the coating zone. After completion of coating, the carrier is returned to its prior position, the substrate holder is lowered onto it and released from the holding mechanism. The carrier with substrate holder is now free to be moved from the coating chamber for further treatment or for unloading through a lock.
A mechanism for this general purpose is disclosed by U.S. Pat. No. 3,662,708 granted May 16, 1972 to R. L. Shrader, and assigned to the same assignee as the present invention. As disclosed, an electromagnet having an energizing and de-energizing coil with conventional control circuits is provided for the pick-up, holding and release of the substrate holder. Although this system is capable of providing positive pick-up and holding force, the use of an electromagnet has certain practical disadvantages such as cost, lack of failsafe features if power is lost, and added complexity of structure, circuit controls, etc.
The present invention is therefore concerned with improvements over the mechanism described above, for providing a simpler, less expensive and more reliable substrate handling mechanism.